A thermal head comprises a plurality of heating elements linearly arranged. A thermal printer enables heating elements of a thermal head to emit heat selectively to make a thermosensitive sheet sense heat or melts the ink of an ink ribbon and transfers the ink to carry out printing.
The heating elements are easily disconnected by the physical impact or thermal abrasion during a printing process. The disconnection of the heating elements causes a bad influence on the printing quality of a thermal printer. Thus, a thermal printer frequently detects the disconnection of the thermal head and confirms the state of the thermal head.
When checking a disconnection, a thermal printer supplies the power to each heating element sequentially and acquires the A/D value of the voltage applied to each heating element. The thermal printer determines whether or not each heating element is in a disconnection state based on the A/D value.
However, the noises contained in the A/D value lead to a reduction in the accuracy in determination on a disconnection state.